Impulse generator



Patented June 4, 1946 IMPULSE GENERATOR William D. Hershberger, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1937, Serial No. 166,685

9 Claims. (Cl. Z50-27.75)

My invention relates to impulse generators employing thermionic'tubes which-are used to generate very high frequency oscillations for very short periods. More specifically, my invention relates to the apparatus for and the method of Another object is to provide means within a generating impulses for radio echo systems. thermionic tube whereby ultra high frequency In Visible obJects nlnay be detected by meanslof 1fiir'slcillalilzion fmay be generated more efficiently radio echoes. An u tra high frequency impu se an ere o ore customary. is transmitted in the form of a beam which is A still further object is to provide means caused to scan the area including an invisible 10 whereby the frequency range in ultra high frebody. The impulse, after striking the body, is requeIlCy OStCrlllatrS may be increased due to a lowected. The reflected impulse is picked up by a ering of e e ectron. transit time. suitable receiver which may belooated near the In describing my invention, reference will be transmitter. The interval between the transmade 150 the accompanying drawing, in which mitted impulse and the received reflected impulse litigure 1 is a schematic diagram of a radio echo is a measure of the distance the impulse has Sys em, traveled from the transmitter to` the reflecting Figure 2 is a graphic illustration of the pulse object and from the reflecting object to the reanddintervlal relation in the impulse generator of ceiver. If the velocity of propagation of the ima ra 1o ec o sys em, pulse is 186,000 miles per second, and if the Figure 31S 8' vieW partly in section of a conventransmitter and receiver are near each other, the Oual liilelljliurlutube. distance in miles from the transmitter to the re` Fleure 4 1s a vlew partly m section of a thernesting objectisequalto mionic tube embodied in my invention, and

186 000 Figure 5 is a schematic circuit diagram of one ---X T embodiment of the impulse generator of my invention. whereTis the intervalinseconds. Referring to Fig. .1, an impulse generator or in, lrdfer theht tranml'fed lllpule Shall trlalnlmittr l i is conected to tipolg antnna 3 n0 m e1 ere W1 e rece Ve lmp 6,1 1S 118C- W c is 00a, ed Wi in a, re ec 0r 'I' e im- SSSaly that the interval between impulses be long pulse 1 is transmitted in the form of a beam along enough to permit the reflected impulse to be rethe line 9 to the object II from which the im- ;'eived befilire a 1hslctlililid inaulse is trarsmtted. pulse is reflected along line I3 to the receiver I5 or examp e, an p se o microsecon s urawhich includes a dipole I and a reflector I9. tion, followed by an interval of 98 microseconds, Fig. 2 illustrates diagrammatically an impulse aiords an optimum range from transmitterto re- 2l which lasts 2 microseconds. The impulse 2l is flecting object of approximately 9.1 miles. At followed by an interval of 98 microseconds, and greater distances, interference would result. thereafter the impulses of 2 microseconds and The range kof the transmitter is a function o1 intervals of 98 microseconds follow each other. the power radiated 1n an impulse- It 1S CilICut I have found that a conventional thermionic tube @efficiently dellVQ the nloulits 0f pOiYel re' 40 operatesI at relatively low average power output qull'ed m th? mammal apphcatlon 0f l @d10 echo when the useful period of oscillation is but two Systems Whlch may Operate at frequencles 0f .the per cent of the total time, as is the case in radio Order 9f 590 megacycles Per second- Ech 1m' echo systems. I have also found that the eilipulse Wilulclude a' tlousand cycs Lfd fre' 5 ciency of thermionic tubes, designed for ultra gsrcgeiod ism'iccgsect 5y arg 1g; high frequency oscillations, falls rapidly as the generators of relatively low efficiencyv at these requncy mcases due to the faclthat etlfcttm; frequencies, but the apparatus becomes most ransft mme comes an apprecla e por lon o cumbersome for mobile operation, aircraft, and a penod' the like. One of the causes for this ineciency A coflventlon thermiofnc Pubs. for genratlflg is the electron transit time within the thermionic 131m; high f1' efquency flscllatlsn; lsshown 11111 Flgtubes. y way o examp e, e u e may ave a one of the Objects of my invention is to procathode 25 which consumes 25 watts and an vide means for generating ultra high frequency anode 21 which disslpates 50 watts. The rated currents during relatively short and widely spaced maximum anode potential is 1250 volts. The osintervals.

Another object is to providemeans in a thermionic tube whereby the ratio of cathode power and plate-dissipated power greatly exceeds the ratio in conventional tubes.

cillatory frequency range does not greatly exceed 3 200-300 megacycles per second, and at the higher frequencies the eiliciency is verylow. The foregoing flgures are based on continuous operation.

In Fig. 4 I have illustrated a thermionic tube which includes within its evacuated envelope 28 a cathode 3|, a grid 33, and an anode 35. The anode 35 preferably includes a number of cooling flanges 31. The envelope 29 is made larger than customary to dissipate larger amounts of heat than has heretofore been customary. The cathode or filament is of a size and of a material which will consume many times the power, and therefore liberate many times the useful emission current. usually required from cathodes, in terms of anode power dissipation.

For tubes using thoriated filament, by way of example, conventional ratios of cathode power to anode-dissipated power are from 1 to 2 to about 1 to 'I and upwards. It should be understood that the emission is proportional to the applied power for a given filament and a given temperature, and while I shall use the term power applied to the cathode for convenience, I am concerned with the thermionic emission.

The thermionic tube of my invention uses the reciprocals of these power ratios. By way of example, the cathode power is from 2 to '7 times, and upward, the power dissipation on plate or anode. Thus. in some tubes suitable for use in my invention, I propose to derive iifty times as much instantaneous emission from the cathode as would be normally required for a given average anode current.

Conventional thermionic tubes for ultra high frequency oscillation may have, by way of example, 1000 to 1250 volts applied to the anode. The efficiency of these tubes decreases with increasing frequency so that it becomes necessary to decrease the anode potential. As the anode potential is decreased, the electron transit time increases and this further limits the frequency. Thus the conventional tube becomes limited by low emciency. and an impassable upper frequency limit.

I propose to apply ten times the anode potential. This will decrease the electron transit time by a factor equal to the square root of ten. The shorter electron transit time will increase the frequency range. Because I shall only apply the anode power for a few per cent of the total time, the anode will be able to dissipate the heat over a relatively long time. The efficiency will be high during the impulse period, and therefore a large amount of energy may be released during the impulse time. Furthermore, since the anode power is only applied for` a small percentage of the time, the source may be designed accordingly.

An application of my invention is shown in Fig. 5. A sinusoidal wave generator 39 is connected to a saw-tooth oscillator 4|. The output circuit of the saw-tooth generator is connected to a limiter !3. The limiter output circuitincludes a biasing battery 'I3 and a resistor 41 which are connected between the cathodes 49 of thermionic tubes ll and a movable bridge member 53. The bridge member 53 is slidably connected to the conductors of the transmission line 58 which ter-` minates ,in the grid electrodes 51 of tubes 5|. The anode electrodes 53 are connected to a transmission line 6| which includes a movable bridge member 83. The bridge member is connected to the positive terminal of a B battery 65. 'I'he negative terminal of the B` battery is joined to radio frequency chokes, which may be in the form 4 of resonant lines. The anode resonant line Il is suitably coupled to a transmission line 01 which terminates in a dipole antenna 39. A reflector 1| may be used to focus the impulses from the Vdipole on the distant reflecting object.

The operation of the circuit is as follows: The thermionic tubes operate in push-pull as oscillators. Parasitic oscillations are prevented by the series resistor which prevents oscillations at a lower frequency since the tubes are effectively in parallel at low frequencies. The frequency of the desired oscillations is determined by the resonant lines.

The anode current is normally blocked by the high bias voltage applied to the grids. The bias voltage is decreased during the oscillatory impulse period by applying positive impulses to the grids. These positive impulses are derived by generating a current of sinusoidal wave form and of the desired frequency. The sinusoidal currents are applied to control the frequency of the saw.. tooth generator which establishes currents of a saw-tooth wave form. The saw-tooth currents are applied to a limiter, which only passes the positive peaks of the saw-tooth current. Since the saw-tooth peaks may be made very sharp, the periods of the impulses may be made short and the intervals between impulses long.

Thus I have described an impulse generato which includes a thermionic tube of novel characteristics. The tube is characterized by a thermionic emission which is many times greater than previously used in tubes of equivalent anode power dissipation. The electron transit time has been greatly shortened by applying high voltages to the anode for short periods, followed by relatively large time intervals. While I have described the impulse generator in connection with a radio echo system, it should be understood that my invention may be applied to telegraphic. telephonic, or directional finding systems.

Iclaim 'as my invention:

l. A thermionic tube of the type wherein the variable output current thereof includes sharp peaks of which vthe time duration per interval does not exceed ten per cent of the period of said interval, said tubing including grid, anode and cathode electrodes therein, said anode having a normal anode current rating, and said cathode having an electron emissive capacity of the order of ten times that required to attain said normal anode current rating.

2. A thermionic tube of the type wherein the variable output current thereof includes sharp peaks of which the time duration per interval does not exceed ten per cent of the period of said interval, said tube including at least anode and cathode electrodes therein, the effective lurface of said anode having a normal anode current rating, and the effective surface of said cathode having an electron emissive capacity of the order of ten times that required to attain said normal anode current rating.

3. A thermionic tube of the type wherein the variable output current thereof includes sharp peaks of which the time duration per interval does not exceed ten per cent of the period of said interval, said tube including at least anode and cathode electrodes therein, said anode having s normal continuous anode current rating, and said cathode having a continuous electron emissive capacity of at least ten times that required to attain said normal continuous anode currentv rating.

4. A thermionic tube of the type wherein the variable output current thereoi' includes sharp peaks of which the time duration per interval does not exceed ten per cent of the period of said interval, said tube including at least anode and cathode electrodes therein, said anode having a normal anode current rating basedupon continu- 'ous operation with a normal cathode, and -said cathode capable of continuous electron emission of at least ten times that required to attain said norma1 anode current rating.

5. A thermionic tube of the type wherein the variable output current thereof includes sharp peaks of which the time duration per interval does not exceed ten per` cent of the period of said interval, said tube including at least anode and cathode electrodes therein, said anode having a normal anode current rating based uponcontinuous operation with a normal cathode, and

said cathode capable of continuous electron emission of from ten to fifty times that required to attain said normal anode current rating.

6. A thermionic tube of the type wherein the variable output current thereof includes sharp.

peaks of which the time duration per interval does not exceed ten per cent of the period of said interval, said tube including grid, anode and cathode electrodes therein, said anode having a predetermined anode current rating, and said cathode having an electron emissive capacity of the order of ten times that required to attain said predetermined anode current rating.

7. A thermionic tube of the type wherein the variable output current thereof includes sharp peaks of which the time duration per interval does not exceed ten per cent of the period of said interval, said tube including at least anode 'and cathode electrodes therein, said anode having a predetermined continuous anode current rating and an intermittent peak current rating of the order of ten times said predetermined current rating, and said cathode having an electron emissive capacity of the order of that required to attain said peak current rating.

8. In a thermionic tube having grid, anode and cathodev electrodes therein, said anode having a normal anodeA current rating, said cathode having an electron emissive capacity of the order of ten times that required to attain said normal anode current rating, the method comprising impressing periodic potentials to said grid, wherein said periodic potentials comprise a peak value and a comparatively low value Der period, said low value extending during at least ninety per centV of said period, and deriving from said anode peak currents exceeding said normal anode current rating by a ratio of the order of at least ten to one.

9. In a thermionic tube having grid, anode and cathode electrodes therein, said anode having a normal anode current rating, said cathode having an electron emissive capacity of the order of ten times that required to attain said normal anode current rating, the method comprising im..

pressing periodic potentials to said grid. wherein said periodic potentials comprise a peak value and a substantially zero value per period, said zero value extending during at least ninety per cent of said period, and deriving from said anode peak currents exceeding said normal anode current rating by a ratio of the order of at least ten t0 one,

WILLIAM D. HERSHBERGER. 

